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  • Perplex
    IB Math AIHL
    /
    Probability
    /

    Bayes' Theorem

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    Bayes' Theorem

    Bayes' Theorem

    Bayes' theorem with 2 and 3 events, sum of conditional probabilities

    Want a deeper conceptual understanding? Try our interactive lesson! (Plus Only)

    Exercises

    No exercises available for this concept.

    Key Skills

    Bayes' Theorem with 2 Events
    AHL 4.13

    Bayes' theorem allows us to reverse conditional probabilities, determining the probability of an event based on prior knowledge of another event. If we have events A and B, Bayes' theorem states:

    P(B∣A)=P(B)P(A∣B)+P(B′)P(A∣B′)P(A∣B)P(B)​📖

    In other words, Bayes' theorem lets us update our beliefs or predictions after observing new evidence. It's particularly useful when dealing with sequential information or adjusting probabilities based on new data.

    Bayes' Theorem with 3 Events
    AHL 4.13

    In some cases, instead of complementary events B and B′, we have complementary events B1​, B2​ and B3​. In this case Bayes' theorem can be generalized to

    P(B1​∣A)=P(B1​)P(A∣B1​)+P(B2​)P(A∣B2​)+P(B3​)P(A∣B3​)P(B1​)P(A∣B1​)​